Many computing systems enable a user to control access to information through passwords, encryption keys, presence settings, and/or other methods. Some online systems enable a user to enter information about the user and enable the user to control whether, how, or which information is accessible to other users. For example, some online systems enable a user to enter a profile of information and establish a group of contacts. Such systems may enable only those contacts to access the profile information and/or detect whether the user is currently logged into an online service, such as a messaging service, a job placement service, or other topic-specific service. The set of contacts comprise a network of people who know a user well enough to provide their contact information. This is sometimes considered a single-level social network.
More broadly, a social network typically comprises a person's set of direct and indirect personal relationships. Direct personal relationships usually include relationships with family members, friends, colleagues, coworkers, and other people with which the person has had some form of direct contact, such as contact in person, by telephone, by email, by instant message, by letter, and the like. These direct personal relationships are sometimes referred to as first degree relationships. First degree relationships can have varying degrees of closeness, trust, and other characteristics. These relationships can also be unidirectional or bidirectional. A unidirectional relationship typically means that a first person is willing and able to interact with a second person, but the second person is not willing or able to interact with the first person. Conversely, a bidirectional relationship typically means that both people are willing and able to interact with each other.
Indirect personal relationships typically include relationships through first degree relationships to other people with whom a person has not had some form of direct contact. For example, a friend of a friend represents an indirect personal relationship. A more extended, indirect relationship might be a friend of a friend of a friend. These indirect relationships are sometimes characterized by a degree of separation between the people. For instance, a friend of a friend can be characterized as a second degree relationship.
Online social network services have developed based on specific topics, such as job placement and dating. These online social network services enable users to connect with each other if they did not previously know each other, but may share a common interest. After a connection is made, the users may view information about each other and/or send messages to each other, but there is little else for the users to do through the online network service. These online network services also generally require a new user to subscribe to the service before the new user has access to any information about other users, even information about an existing user that invites the new user to join the online service.